A flat belt conventionally used as a high-speed transmission belt is generally made into an endless belt by processing opposite ends of a band-shaped belt having a polyamide film as a core body into a joint shape, such as a skiver joint and a finger joint, followed by integrally adhering with an adhesive or thermal adhesion.
However, because the adhesive usually has poor flexibility, the belt may be partially hardened at a joint part and stress concentration is apt to occur at the hardened portion, and consequently the durability, particularly bending resistance of the belt is apt to deteriorate. Cracks can occur at the joint part in a short period of time. In some cases, the belt can be broken.
When manufacturing a paper tube, the paper tube is manufactured by spirally winding a paper tape 41 around a mandrel 42 as shown in FIG. 14. The paper tape 41 wound around the mandrel 42 is transported in an axial direction by a flat belt 43 (Patent Document 1). The flat belt 43 is to be strongly twisted and functions to perform pressure contact and delivery of base paper of the paper tube with an adhesive applied thereto.
Thus, the flat belt 43 used for manufacturing the paper tube is wound around the paper tape while being strongly twisted, and travels at high speed while performing the pressure contact. Therefore, a middle part of the belt and a side end part thereof differ from each other in elongation rate, specifically the side end part has a larger elongation rate than the middle part, and consequently the joint part may break under load.
The flat belt used for manufacturing the paper tube needs to be wound around the paper tube at a certain angle and travel while being pressure contacted to the paper tube. Hence, uneven winding pressure is apt to occur. When high pressure contact is performed by further increasing the tension of the belt in order to eliminate the uneven winding pressure, the belt has shorter service life due to uneven wear, and the belt may break in some cases. Additionally, the increased tension of the belt increases load on a mechanical side and, for example, the belt is strongly wound around the mandrel for winding the paper tape, thus leading to an early wear of the mandrel. The paper tube of poor quality may occur, or the mandrel may need to be replaced in a short period of time. Furthermore, the strong winding of the belt increases power consumption, thereby increasing running costs. Even when the belt is merely softened to improve winding performance, deformation volume of the belt may increase because the belt is strongly twisted. Consequently, uneven wear may occur due to friction between the belts, resulting in short service life.
Meanwhile there is an endless flat belt without any joint part. According to a conventional method therefor, opposite ends of a reinforcement fabric are jointed together and overlaid on an outer surface of a cylindrical metal mold corresponding to a belt size, a cord core is wound around the reinforcement fabric, and a rubber sheet or the like is overlaid thereon, followed by vulcanization molding. The endless flat belt has the advantages that the belt has no joint therein and has excellent bending resistance.
However, when the endless flat belt is used for the purpose of a twist travel, such as the paper tube winding machine as described above, due to the difference in elongation rate between the middle part and the side end part of the belt, the side end part elongates farther than the middle part, so-called one-sided elongation occurs, and the belt is apt to be wavily deformed. Upon the occurrence of the one-sided elongation, it is difficult to uniformly apply a tension in a width direction of the belt. There are the problems that a winding force of the paper tube onto the base paper becomes uneven, and the travel of the belt becomes unstable.
As a method for manufacturing the endless flat belt, materials are laminated one upon another on an outer surface of a cylindrical metal mold and are then subjected to belt molding. Therefore, a circumferential length of the belt depends on a circumferential length of the metal mold, and there is the need to have the cylindrical metal mold for each circumferential length. Patent Documents 2 and 3 respectively disclose endless belts in which a tubular flat knitted fabric (circular knitted fabric) is entrained in a stretched state between two rolls, and a cord core is wound at a constant pitch in the width direction of the belt and adhered integrally. The above problems cannot occur because there is no joint part of the reinforcement fabric. With this method, it is, however, difficult to manufacture various endless flat belts that differ in length because the circumferential length of the belt is determined by the circumferential length of the tubular flat knitted fabric to be used. Particularly, it is difficult to manufacture a belt having a large circumferential length.
Meanwhile, for example, for the purpose of the paper tube winding machine whose circumferential length is as long as approximately 7-9 m, there is a demand for a belt free from any joint and the one-side elongation.